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Finding peak of a centrally peaked array in JavaScript
Centrally Peaked Array
We call an array arr a centrally peaked array if the following properties hold −
arr.length >= 3
There exists some i with 0 < i < arr.length - 1 such that
arr[0] < arr[1] < ... arr[i-1] < arr[i]
arr[i] > arr[i+1] > ... > arr[arr.length - 1]
Problem
We are required to write a JavaScript function that takes in an array of numbers, arr, as the first and the only argument.
The input array is a centrally peaked array. Our function is supposed to return the peak index of this centrally peaked array.
For example, if the input to the function is
Input
const arr = [4, 6, 8, 12, 15, 11, 7, 4, 1];
Output
const output = 4;
Output Explanation
Because the element at index 4 (15) is the peak element of this array.
Example
Following is the code −
const arr = [4, 6, 8, 12, 15, 11, 7, 4, 1];
const findPeak = (arr = []) => {
if(arr.length < 3) {
return -1
}
const helper = (low, high) => {
if(low > high) {
return -1
}
const middle = Math.floor((low + high) / 2)
if(arr[middle] <= arr[middle + 1]) {
return helper(middle + 1, high)
}
if(arr[middle] <= arr[middle - 1]) {
return helper(low, middle - 1)
}
return middle
}
return helper(0, arr.length - 1)
};
console.log(findPeak(arr));Output
4
Updated on: 24-Apr-2021
244 Views
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